Magnetic coupling device



y 4, 1957 w. H. WICKERSHAM 2,792,093

MAGNETIC COUPLING DEVICE Original Filed Nov. 29, 1951 FIG. 1

FIG. 3

INVENTOR. Wl LFR ED H .WICKERSHAM HTTOK/VEV United States Patent OMAGNETIC COUPLING DEVICE Wilfred H. Wickersham, Nutley, N. .l., assignorto Bendix Aviation Corporation, Teterboro, N. .L, a corporation ofDelaware Continuation of application Serial No. 258,923, November 29,1951. This application September 26, 1955, Serial No. 536,534

2 Claims. (Cl. 192-215) This invention relates to magnetic couplingdevices. More particularly, the invention relates to magnetic couplingdevices of the magnetic drive type or magnetic clutches, and especiallymagnetic particle clutches, for drivably coupling together a drivingmember and a driven member. This application is a continuation-in-wholeof my copending application Serial No. 258,923, filed November 29, 1951,now abandoned.

The conventional approach in the formation of magnetic particle clutchesis to provide two coupling members, usually two parallel discs orconcentric cylinders, each rotatable independently of the other about acommon axis. The coupling member connected to the power source is calledthe driving member while the coupling member connected to the load iscalled the driven member or rot-or. In the region between the couplingmembers, amixture of finely powdered iron and solid lubricant isretained which efiectively solidifies under the influence of themagnetic field established by an associated electromagnet coil. In thepresence of this magnetic field, the solidified mixture by magneticattraction and the resultant frictional wedging action between thecoupling members introduces restraining forces which effectively bindtogether the two coupling members and thereby engage the clutch.

Heretofore, it has been customary to make both coupling members offerromagnetic material because of the relatively low reluctance which amagnetic driven member introduces into the magnetic circuit. In clutchdrive applications, particularly those directed to servo systems, thespeed of response of a clutch is often of prime importance and isdetermined by two principal factors: the electrical constants of thecoil establishing the magnetic field and its associated circuit, and thedynamic mechanical constants of the moving or coupling members of theclutch. Of particular interest in this instance are the dynamicmechanical constants, the most important of which are the force ortorque developed and the inertia of the load or driven member. Incertain prior constructions one of the magnetic coupling members, forexample the driven member in clutch drive applications, was providedwith a limited number of holes in an effort to reduce weight and inertiaand in order to minimize caking of the mixture when the electromagnetfield coil was deenergized. Although in such construction some of themagnetic lines of force and solidified links of the mixture may extendfrom one magnetic pole through the holes to the other pole to produce aninterlinking action, the remaining majority of links follow theremaining majority of magnetic lines of force which extend from one poleto the other via paths through the solid portions of the magnetic drivenmember which otter less magnetic reluctance than the hole gap. Theprovision of holes in the magnetic driven member limits the amount oftorque which may be developed, since the field gap is effectivelylengthened which decreases the field gradient strength. It will thus beseen that in constructions employing a magnetic driven member with holesthe development of torque depends principally upon the phenomenon ofmagnetic attraction and frictional wedging action and secondarily littleupon the phenomenon of interlinking action. In prior constructions,magnetic driven members with a limited number of slots were tried andabandoned as unsuccessful. Prior to the present invention, there were noknown magnetic coupling devices employing one non-magnetic cup-shapedmember wherein the rim portion was provided with selected apertureslocated in the magnetic field of the other member so as to receive aprincipal number of the solidified links of the magnetic mixture wherebythe total coupling action or total torque is produced principally by thephenomenon of interlinking action rather than by the phenomenon ofmagnetic attraction or wedging action.

It is an object of the present invention to provide an improved magneticcoupling device.

It is another object of the invention to provide an improved magneticdrive coupling device and to provide an improved magnetic particleclutch.

it is another object of the invention to provide an improved magneticparticle coupling device based upon a new phenomenon and mode ofoperation wherein one of the coupling members has a novel non-magneticapertured portion located in the field gap of the other coupling memberfor improving the operating characteristics of such device.

It is another object of the invention to provide a novel magneticparticle clutch employing an apertured nonmagnetic driven member so asto have lower mass and inertia and faster response and yet constructedso as to transmit relatively high torques comparable with the torquestransmitted by magnetic particle clutches having magnetic driven membersof similar dimensions.

It is a further object of the invention to provide a novel magneticparticle coupling device wherein one of the coupling members has anon-magnetic portion having selected apertures located in the magneticfield gap of the other coupling member and wherein the total couplingaction or total developed torque is due principally to a phenomenon ofinterlinking action by solidified links extending through the aperturesrather than to a phenomenon of frictional wedging action by solidifiedlinks of magnetic particles wedged between opposed surfaces of thecoupling members.

'It is a further object of the invention to provide a novel magneticparticle device wherein one of the coupling members has a non-magneticportion having apertures located in the magnetic field gap of the othercoupling member and wherein the apertures have a selected geometry anddistribution such that there is an optimum relationship between totalaperture area and total area of the intervening solid parts of suchnon-magnetic position which define the apertures, whereby an optimumnumber of the solidified links of magnetic particles make direct contactwith such intervening solid parts to yield relatively high couplingaction or torque.

It is a further object of the invention to provide a successfullyoperable'magnetic coupling device employing a novel slotted member ofnon-magnetic material as one of the coupling members, the slots beinglocated in the magnetic field of the other coupling member.

The above and other objects and advantages of the present invention willappear more fully hereinafter from a consideration of the detaileddescription which follows taken together with the accompanying drawingwherein one embodiment of the invention is illustrated.

In accordance with one aspect the present invention contemplates amagnetic coupling device comprising two. relatively rotatable couplingmembers coaxial about a common longitudinal axis, the first couplingmember being composed of magnetic material and having annular surfacesdefining an annular gap, and means are provided for producing a magneticfield between the annular surfaces and traversing the gap. The secondcoupling member has an annular rim portion of non-magnetic material,such as aluminum, and extends into the gap, the rim portion beingprovided with a series of discrete apertures located in the gap so as tobe in the magnetic field. A quantity of discrete relatively movablemagnetic particles disposed in the gap and in the series of aperturesand form links of mutually attracted or solidified magnetic particlesattracted to the annular surfaces of the first member and extendingtherebetween across the annular gap and through respective of theapertures under the influence of the magnetic field to link the couplingmembers together. The apertures preferably have a geometry anddistribution selected to produce an optimum total aperture area, ascompared with the total area of the non-aperturcd rim portionsintervening between the apertures, whereby an optimum number of thesolidified links in the apertures make active direct contact with theedge of such non-apertured intervening rim portions to contribute to thecoupling action, and accordingly the total torque or total couplingaction between the members is relatively large and is due principally,and preferably entirely, to the links of solidified magnetic materialextending through such apertures rather than to frictional wedgingaction. The series of apertures are preferably in the form of a seriesof discrete rectangular slots extending along the longitudinal axis ofthe device and distributed around the circumference of the rim portion,the slots being formed by a series of thin ribs or rib portionsextending longitudinally and distributed around the circumference of therim portion. The circumferential extent or width of each slot ispreferably greater than the circumferential extent or width of each ribso that a maximum number of solidified links of magnetic particles areable to actively engage the edges of the ribs to contribute to the totalcoupling action or torque.

The present invention in another aspect contemplates a magnetic couplingdevice incorporating a novel rotor having a portion made of anon-magnetic light-weight material, such as aluminum, with selectedholes or slots formed in such portion and located in the field gap ofthe other coupling member so as to provide a predeterrnined relativelylarge transmitted torque. In this manner, it is possible to obtain atorque output from a clutch employing a non-magnetic rotor which iscomparable with that obtained with a ferromagnetic rotor of similarphysical dimensions. In addition, an appreciable reduction in mass androtational inertia can be effected. Since acceleration is inverselyproportional to inertia for the same applied torque, this reduction ininertia appears externally as increased acceleration or speed ofresponse. This is very desirable for many servo applications where theperformance, when using this power clutch drive, is limited by therestrictions imposed by the rotational inertia of the relatively massiveiron rotor. In addition, the problem of damping or stabilizing a servosystem employing the low inertia rotor is appreciably simplified.

In the drawing, wherein like reference characters refer to like partsthroughout the several views;

Fig. l is an elevational view, in section, of the magnetic particleclutch embodying the present invention;

Fig. 2 is a rear elevational view of the cup-shaped nonmagnetic rotorused with the clutch of Fig. l; and

Fig. 3 is a section of the non-magnetic rotor taken along line 33 ofFig. 2.

Referring now to the drawing for a more detailed description of thepresent invention, and more particularly to Fig. 1 wherein oneembodiment hereof is clearly illustrated, a magnetic particle clutchgenerally designated-by the numeral 11 comprises a ferromagnetic drivingmember 12 which includes a cylindrical-shapedmember 14 closed off at itsends by a circular plate 16 and a nonmagnetic plate 18, the plates beingsecured to member 14 by screws 20. Driving member 12 is mounted forrotation on a shaft 22, which extends therethrough, by a pair ofbearings 24 retained in plates 16 and 18. Secured to plate 16 by screws26 is a soft iron core or coil supporting member 28 which accommodatesan energizable winding 30. Member 14 and core 28 have opposed and spacedcircular face portions 32 and 34, respectively, which define an airgap36. Face portions 32 and 34 define opposed magnetic pole faces for themagnetic field across airgap 36 which is produced when winding 30 isenergized.

Extending into airgap 36 is the peripheral rim portion 38 of acup-shaped rotor or driven member 39 which is made of a non-magneticlight weight metal, such as aluminum. Rotor 39 is fixed to shaft 22 by akey 41 which is secured to the shaft and projects into a slot 42 formedin a hub 43 of the rotor. The body or base 45 of rotor 39 is located ina chamber 47 which communicates with airgap 36; the chamber beingdefined by the inside walls of member 14, plate 18 and core 28.Peripheral rim portion 38 is formed at right angles to base 45 and, asshown in Fig. 3, has formed therein in distributed relation around thecircumference of the rim a series of elongated and parallel arrangedslots or openings 49 bounded on either side by ribs 50. As shown in Fig.3, the ribs are thin and the circumferential extent or width of eachslot is substantially greater than the circumferential extent or widthof each rib, whereby the total slot area is substantially greater thanthe total rib area and accordingly the driving torque developed in rotor39 will be due substantially entirely to the phenomenon of interlinkingaction by the links of magnetic bonding material extending through theslots under the influence of the field rather than by frictional wedgingaction of any links wedged between solid portions of the rim 38 and thepole faces. In accordance with a feature of the invention the uniquegeometrical configuration of slots shown in Fig. 3 provides an optimumratio of aperture area to intervening solid portion area in thenonmagnetic rim so that an optimum number of links of magnetic materialmake active direct contact with solid portions of the rim for maximumdriving torque.

In order to provide the driving connection between rotor 39 and drivingmember 12, a ferromagnetic bonding material or powdered mixture 52 isarranged in the airgap which is adapted to be solidified when a magneticfield traverses the airgap. Bonding material 52 is a mixture of powderediron and powdered graphite, the percentage by weight being preferably,though not necessarily, of the order of 20 to 1, respectively. Thegraphite serves as a lubricant for the powdered iron and is known toeasily attach to the metal surfaces. The mixture is dust-like andfiowable in character and is arranged in the airgap, and consequently,in the slotted portion of rim 38. When winding 30 is energized, bondingmaterial 52 becomes solidified and firmly secures together rotor 39 anddriving member 12. It is believed that the establishment of a magneticfield in the airgap containing the mixture causes links or chains toform therein which extend through openings 49 and engage the edges ofrespective ribs 50 defining the respective slots 49, the links havingopposite ends terminating on opposed faces 32 and 34. According to theresults obtained, it appears that ribs 50 of rim 38 tend to cut throughthe links as the driving member is rotated, but are restrained fromdoing so under no-slip conditions due to the rigidity of the links.Since the ribs cannot cut through the links under no-slip conditions,rotor 39 will be coupled to and carried along with the driving member torotate shaft 22 which is connected to the load. In this manner, thelinks cooperate with the ribs to effect a sturdy coupling connection.

Due to the dust-like and flowable characteristics of-the mixture whenwinding 30 is deenergized, means must be provided to direct theparticles which leave the gap, back into the airgap and also, to preventthe iron particles from entering the bearings and scoring them. Novelbaffie means are provided, which. comprise a pair of discs 55 and 56secured to opposite walls of chamber 47, that is, to the adjacent wallsurfaces of plate 18 and core 28, respectively. Discs 55 and as haveformed integrally thereon concentrically arranged circular lip-portions58 which project upwardly and in a direction away from the centers ofthe discs. Cooperating with lip portions 58 on discs 55 and 5d aresimilarly formed lip-portions 60 on both sides of rotor base 45. Lips 58and 60 are staggered with respect to each other so that a deviated pathis provided for the magnetic particles falling out of the airgap. Sincethe lips extend toward the airgap (Fig. 1), rotation of the drivingmember will cause the magnetic particles to be directed toward and intothe airgap by centrifugal action. At the same time, lips 58 and 6t serveto obviate leakage of the mixture from driving member 12 because of theresistance presented to the flow of particles by the staggered barrier.Additional means for preventing leakage of the mixture into the bearingsare provided in the form of interfitting annular rings which comprisethe labyrinth seal 62 adjacent bearing 24 in plate 13. With thearrangement described above, the life of the bearings is lengthenedconsiderably and replacement thereof is infrequent.

As seen in Fig. 1, rotation of driving member 12 is accomplished by wayof a bevel gear 65 which is secured to member 12 and the gear is rotatedby a companion bevel gear (not shown). Inasmuch as it is desired for agiven developed torque to increase the speed of response of rotor 39,openings 65 are cut in base 45 (Fig. 2) adjacent the peripheral edgethereof, thereby efiecting an added decrease in rotational inertia ofthe rotor. Moreover, openings 65 provide for circulation of the mixtureon both sides of the base so that the particles may be more readilytransmitted therethrough and toward the airgap i. e. Without becomingpacked in.

It will now be readily apparent that the present invention provides animproved magnetic coupling device and particularly an improved magneticparticle clutch utilizing novel rotor means based upon a new phenomenonand mode of operation which provides relatively high torque and yetdecreases the mass and inertia and time of response of the device,thereby making it of increased value in servo systems. The employment ofa cup-shaped non-magnetic lightweight rotor for low inertia and yetcapable of developing a required high torque is made possible by thenovel apertured arrangement, preferably slotted, formed in theperipheral rim portion thereof, whereby an effective connecting bondresults to increase the magneto-mechanical coupling of the driving anddriven members. The utilization of the described baffie means in amagnetic particle clutch effectively retards leakage of the bondingmaterial from the self-enclosed driving member. Moreover, the bafllemeans aids in directing the magnetic particles into the airgap.

Although one embodiment of the invention has been illustrated anddescribed in detail, it is to be expressly understood that the inventionis not limited thereto.

Various changes can be made in the design and arrangement of the partswithout departing from the spirit and scope of the invention as the sameWill now be understood by those skilled in the art.

I claim:

1. A magnetic coupling device comprising first and second relativelyrotatable coupling members coaxial about a common longitudinal axis,said first coupling member being composed of magnetic material andhaving annular surfaces defining an annular gap, means for producing amagnetic field between said annular surfaces traversing said gap, saidsecond coupling member having an annular rim portion of non-magneticmaterial extending into said gap, said rim portion having a series ofsubstantially parallel ribs extending along said longitudinal axis anddistributed around the circumference of said rim portion, said ribsdefining therebetween a series of longitudinally extending slots locatedin said gap so as to be in said magnetic field, the circumferentialextent of each of said slots being of the same order as thecircumferential extent of each of said ribs, and a quantity of relatively movable magnetic particles in said gap and in said series of slotsand adapted to form links of mutually attracted magnetic particlesattracted to said annular surfaces and extending therebetween acrosssaid annular gap and through respective of said slots under theinfluence of said magnetic field to link said coupling members together.

2. A magnetic coupling device comprising first and second relativelyrotatable coupling members coaxial about a common longitudinal axis,said first coupling member being composed of magnetic material andhaving annular surfaces defining an annular gap, means for producing amagnetic field between said annular surfaces traversing said gap, saidsecond coupling member having an annular rim portion of non-magneticmaterial extending into said gap, said rim portion having a series ofsubstantially paraL lel ribs extending along said longitudinal axis anddistributed around the circumference of said rim portion, said ribsdefining therebetween a series of longitudinally extending slots locatedin said gap so as to be in said magnetic field, the circumferentialextent of each of said slots being larger than the circumferentialextent of each or" said ribs, and a quantity of relatively movablemagnetic particles in said gap and in said series of slots and adaptedto form links of mutually attracted magnetic particles attracted to saidannular surfaces and extending therebe tween across said annular gap andthrough respective of said slots under the influence of said magneticfield to link said coupling members together.

OTHER REFERENCES Technical Report 1213, National Bureau of Standards,Washington, D. C. Copy received in U. S. Patent Oflice on March 30,1948.

